The Little Friend. Tartt D.

One day is never, ever discussed by the Cleve family. The day that nine-year-old Robin was found hanging by the neck from a tree in their front garden. Twelve years later the family are no nearer to uncovering the truth of what happened to him. Inspired by Houdini and Robert Louis Stevenson, twelve-year-old Harriet sets out to find her brother's murderer - and punish him. But what starts out as a child's game soon becomes a dangerous journey into the menacing underworld of a small Mississippi town.